THE PLANT. 65 



food in soluble form and carry it to the stem or other parts of 

 the plant for assimilation. 



When all other essential factors are present, the limit of 

 plant growth will depend upon the conditions of the water supply. 

 The amount of water required by certain plants to perform their 

 normal functions is one of the important studies of agriculture. 



The amount of water contained in different plants, or in the 

 same plant at different stages of growth and maturity is subject 

 to great variation. 



NOTE. For water content of various foods, see table page 368. 



Functions of Water in Plant Life. 



1. Water carries dissolved minerals into the plant. 



2. It forms an essential part of plant food. 



3. It is the medium of vital processes in plant growth. 



4. It cools the plant by evaporation. 



The amount of water transpired by plants is remarkable. 

 From 250 to 400 pounds of water is transpired for every pound 

 of dry matter produced. 



PROBLEM. 



1. Estimated from the transpiration of a small plant, an apple tree 

 30 years old would evaporate 36,000 pounds of water in one growing 

 season; how many tons of water would be transpired by an acre of 

 40 such trees in one season? 



The Root System. 



The entire mass of roots belonging to a plant is called its 

 root system. Some idea of the importance of the root system of 

 a plant may be gained, when it is estimated that if all the roots of 

 a thrifty corn plant were placed end to end they would reach a 

 mile. This shows the importance of studying the subject of 

 moisture supply and the effects of deep and shallow cultivation. 

 This great root system is dependent upon every root to perform a 

 function necessary for maximum results. 



The part of a plant above ground will usually indicate the 

 condition and the extent of its root system. 



